Well if u define the Colum as Primery Key, It will create Clustered Index by default. If the colum is not Primery key, then its better create Non clustered Index on that with fill factor between 65 - 80.
You can create clustered index using Index Wizard in Enterprise Manager (Tools -->> Wizards ) also.
Creating clustered index slows down Insert,Update and Delete actions but no doubt improves read speed as the data is already in sorted mode and so SQL doesn't have to go to TempDB. Howevre If your table has a Primary Key colum, then u can't create clustered index on that table on other colum. If its a must case, then U have to drop the Clustered Index related to Primary key Colum and then only u can create clustered index on other colum.
CREATE CLUSTERED INDEX IND_CL_COL1 ON TABLE1 (COL1 ACS)
WITH FILL FACTOR =75
**IND_CL_COL1 is name of index
** FILL Factor may vary a little.